In the sentence "This is the very thing I want," the word 'very' functions as an emphasizing adjective.

Here's why:

• Emphasizing adjective: This type of adjective intensifies the meaning of another adjective or adverb. In this case, "very" emphasizes the importance of "thing" being exactly what the speaker wants.
• Exclamatory adjective: These adjectives express strong emotions like surprise or excitement. "Very" doesn't convey such emotions here.
• Compound adjective: This combines two or more words to act as a single adjective. "Very" isn't part of a compound adjective here.
• Adjective of quality: These describe the inherent qualities of a noun. "Very" doesn't describe the quality of "thing" itself.
• Adjective of quantity: These indicate how much or how many of something there is. "Very" doesn't quantify anything in this sentence.

By emphasizing the importance of "thing," "very" strengthens the expression of the speaker's desire.